1. Field of the Invention
The present invention relates to a clutch apparatus for controlling two-phase positions of a rotating body.
2. Description of the Related Art
Generally, in the case of a laser color printer, a plurality of developing units for developing an image for each color is installed around a photoconductive medium. Therefore, if the developing unit for each color sequentially forms a color image on the photoconductive medium, the formed color images are sequentially transferred to and overlapped on a transferring belt. After that, the overlapped color images formed in such a manner are transferred to a transferring roller rotated by contacting the transferring belt and a paper passing through the transferring belts and the transferring roller. Finally, a paper on which the color image is transferred is discharged after passing through a fixing unit. The laser color printer operating in such a manner has a cam operating apparatus capable of separating the transferring roller from the transferring belt while the color images are formed and overlapped on the transferring belt, and of bringing the transferring roller into contact with the transferring belt so that the color images are completely formed and overlapped.
Also, the cam operating apparatus selectively operates on or off with the help of a clutch apparatus capable of controlling two-phase positions, thereby controlling a position of a member such as the transferring roller for which two-phase position control is required.
FIG. 1 shows a conventional clutch apparatus for two-phase position control, which includes: an axis part 10 on which a shaft 12 having a cam 11 is fixed; a driving gear 13 having a spring clutch (not shown) intervened, for being selectively rotatable with respect to the axis part 10; and a solenoid 20 on which the axis part 10 is supported in a rotatable manner, for controlling rotational position by selectively providing a load on the axis part.
According to the foregoing construction, if the solenoid 20 is turned on, while the driving gear 13 and the shaft 12 are rotated together by clutch operation, the first phase protuberance 10a projected on the outer periphery of the axis part 10 is hooked by a switch member 21 of the solenoid 20 as shown by a virtual line. Thus, at this status, the first phase of the cam 11 is position-controlled.
Also, in order to perform position control for the second phase of the cam 11 by rotating the cam 11 as much as 180 degrees, the solenoid 20 is turned off. Then, the switch member 21 is moved to a position as shown by a solid line. After that, while driving gear 13 is rotated together with the shaft 12 and the axis part 10, the second phase protuberance 10b is hooked by the switch member 21. At that moment, rotation of the shaft 12 is stopped by clutch operation. By such operation, the second phase of the cam 11 is position-controlled.
The conventional clutch apparatus having the foregoing construction should constantly maintain the solenoid at its on-status in order to maintain any position out of two phase-positions. In that case, power consumption increases constantly, and the solenoid 20 is overheated, so that magnetic force weakens and the sticking force of the switch member 21 deteriorates. Therefore, there may occur a case that position control is not properly performed. Also, the switch member 21 is magnetized, so that the separating time is lengthened when the solenoid is turned off, whereby exact cam operation is not appropriately performed.